[url_launcher] Adds macOS package with example app

[franciscojma86]

Description

Adds the macos implementation of the url_launcher plugin.
Tested by adding an example app that runs the e2e tests. This example app is a copy of the url_launcher/example app, with a modified pubspec.yaml that depends on url_launcher from pub, and url_launcher_macos from path. There is also a minor change in main.dart where the last widget is removed since there is no macOS implementation for that method.

The Swift implementation of the plugin was ported from https://github.com/google/flutter-desktop-embedding/tree/master/plugins/flutter_plugins/url_launcher_fde

Related Issues

flutter/flutter#41721

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[amirh]

Can you mention in the PR description that the example app is a copy of the one for url_launcher and call out what has changed (pubspec.yaml and main.dart?)

I'm not qualified to review the Swift code, so RSLGTM for that part.

[amirh]

Should this be the the standard license header we use?

[franciscojma86]

Yeah, updated

[amirh]

LGTM

[domesticmouse]

Any idea when this will be published on pub.dev? I have a desktop sample app in progress that uses url_launcher and I'd love to drop the reference to url_launcher_fde.

[franciscojma86]

@domesticmouse It is on pub.dev now, but not endorsed yet. You can still use it though.

[domesticmouse]

@franciscojma86 I have no idea what endorsed means, but using url_launcher: ^5.3.0 without url_launcher_fde results in a macOS desktop binary that throws MissingPluginException (MissingPluginException(No implementation found for method canLaunch on channel plugins.flutter.io/url_launcher))

[franciscojma86]

Endorsed means that you would just be able to use url_launcher: ^5.3.0 and should work, but in this case you have to do a bit more. Try adding to your pubspec:

url_launcher: ^5.3.0
url_launcher_macos: ^0.0.1